A large class of books is made with a single-layer paper cover glued or otherwise attached to the spine. These are commonly referred to as a paperback book. Many of the paperback books in current use experience long term retention and use. For example, college textbooks, telephone directories and many others may remain in use for months or years under constant handling. It is common experience that the covers of paperback books soon become frayed, tattered, torn, stained or removed completely.
The prior art contains a number of attempts to provide covering and reinforcement for paperback book covers. Typical of these attempts are the inventions disclosed in U.S. Pat. Nos. 3,140,883; 3,165,337; 3,241,863; 3,572,767 and 3,915,778 in which the original paper cover of a book is fitted into an envelope-type pocket usually sealed on three edges and sometimes reinforced with a reinforcing board. In some of these patents, the two pockets are independently slipped over the front and back covers and are held in place by adhesive tape bonding to the book or bonding to each other.